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Hydrogeology Journal

, Volume 26, Issue 7, pp 2459–2473 | Cite as

Groundwater hydrodynamics and salinity response to oceanic tide in coastal aquifers: case study of Sahel Doukkala, Morocco

  • Ahmed FadiliEmail author
  • Philippe Malaurent
  • Saliha Najib
  • Khalid Mehdi
  • Joëlle Riss
  • Abdelhadi Makan
Paper

Abstract

Seasonal variations of sea level have an important impact on coastal groundwater level and salinity. Consequently, they cause spatiotemporal changes in the seawater/freshwater interface. The oceanic tide effect on groundwater dynamics and salinity was investigated in the coastal aquifers of Sahel Doukkala, Morocco. Continuous monitoring of water level and electrical conductivity (EC) was carried out in two coastal wells (drawing from two different aquifers) over a period of 9 months. The main objective of the study was to characterize the aquifers’ exposure to anthropic pumping operations and oceanic tide oscillations. The obtained results showed that oceanic tide has a significant effect on groundwater level as well as on water salinity. The fluctuation periods of groundwater level and tidal level were found to be equal, with a specific time lag. Hydraulic diffusivity was calculated using both confined- and semi-confined-aquifer methods and by analyzing both the time lag and amplitude damping factor. Results indicate hydraulic diffusivity differences between the two aquifers. In addition, there were apparent differences depending on whether time lag or amplitude was analyzed, possibly due to effects of heterogeneity within the aquifers. A detailed study of water EC variation revealed the significant influence of daily and synodic tide on groundwater salinity. Water EC variations were significant when hydraulic diffusivity is higher, indicating that sea-level oscillations induce freshwater/seawater interface movement and consequently influence the groundwater quality.

Keywords

Groundwater monitoring Hydraulic diffusivity Electrical conductivity Salt-water/fresh-water relations Morocco 

Influence des marées océaniques sur l’hydrodynamique et la salinité des eaux souterraines d’aquifères côtiers: cas d’étude du Sahel des Doukkala (Maroc)

Résumé

Les variations saisonnières du niveau de la mer ont un impact important sur le niveau et la salinité des eaux souterraine côtières. En effet, elles provoquent des modifications spatio-temporelles de l’interface eau salée/eau douce. L’effet de la marée océanique sur la dynamique et la salinité des eaux souterraines a été étudié pour les aquifères côtiers du Sahel des Doukkala, au Maroc. Un suivi en continu du niveau piézométrique et de la conductivité électrique (CE) a été mis en place au droit de deux puits côtiers (captant deux aquifères distincts), durant une période de 9 mois. L’objectif principal de cette étude était de caractériser l’impact des pompages et des oscillations océaniques des marées sur les aquifères. Les résultats obtenus ont montré que la marée océanique a une influence significative sur le niveau piézométrique, de même que sur la salinité de l’eau. Les périodes de fluctuation du niveau des eaux souterraines et du niveau de marée sont apparues identiques, avec un décalage temporel spécifique. La diffusivité hydraulique a été calculée en utilisant à la fois les méthodes pour un aquifère captif et semi-captif, et en analysant le décalage temporel et le facteur d’atténuation de l’amplitude. Les résultats indiquent des différences de diffusivité hydraulique entre les deux aquifères. De plus, des différences apparaissaient selon que l’analyse portait sur le décalage temporel ou sur l’amplitude, possiblement à cause des effets de l’hétérogénéité au sein des aquifères. Une étude détaillée des variations de la CE de l’eau a révélé l’influence significative de la marée journalière et synodique sur la salinité des eaux souterraines. Les variations de la CE de l’eau étaient significatives pour une diffusivité hydraulique plus élevée, indiquant que les oscillations du niveau marin induisent un déplacement de l’interface eau douce / eau salée, et par conséquent influence la qualité des eaux souterraines.

Hidrodinámica del agua subterránea y respuesta de la salinidad a la marea oceánica en acuíferos costeros: estudio del caso de Sahel Doukkala, Marruecos

Resumen

Las variaciones estacionales del nivel del mar tienen un impacto importante en el nivel y en la salinidad del agua subterránea costera. En consecuencia, provocan cambios espaciotemporales en la interfaz agua de mar/agua dulce. El efecto de la marea oceánica sobre la dinámica y la salinidad del agua subterránea se investigó en los acuíferos costeros de Sahel Doukkala, Marruecos. El monitoreo continuo del nivel del agua y de la conductividad eléctrica (EC) se llevó a cabo en dos pozos costeros (procedentes de dos acuíferos diferentes) durante un período de 9 meses. El objetivo principal del estudio fue caracterizar la exposición de los acuíferos a las operaciones antrópicas de bombeo y a las oscilaciones de las mareas oceánicas. Los resultados obtenidos mostraron que la marea oceánica tiene un efecto significativo en el nivel del agua subterránea y en la salinidad del agua. Los períodos de fluctuación del nivel del agua subterránea y el nivel de la marea se encontraron iguales, con un retraso de tiempo específico. La difusividad hidráulica se calculó utilizando métodos para acuíferos confinados y semi confinados y analizando tanto el desfase temporal como el factor de amortiguación de la amplitud. Los resultados indican diferencias de difusividad hidráulica entre los dos acuíferos. Además, hubo aparentes diferencias dependiendo de si se analizó el desfase temporal o la amplitud, posiblemente debido a los efectos de la heterogeneidad dentro de los acuíferos. Un estudio detallado de la variación de la EC del agua reveló la influencia significativa de la marea diaria y sinódica sobre la salinidad del agua subterránea. Las variaciones de EC en el agua fueron significativas cuando la difusividad hidráulica es más alta, lo que indica que las oscilaciones del nivel del mar inducen el movimiento de la interfaz agua dulce/agua de mar y, en consecuencia, influyen en la calidad del agua subterránea.

沿海含水层地下水动力学及含盐度对海洋潮汐的响应:摩洛哥Sahel Doukkala研究案例

摘要

海平面季节性变化对沿海地下水位和含盐度有重要的影响。因此,这些变化可引起海水/淡水界面的时空变化。调查了海洋潮汐对摩洛哥Sahel Doukkala沿海含水层地下水动力学和含盐度的影响。在9个月的时间内对两口沿海井(两个不同的含水层)的水位和电导率进行了连续监测。研究的主要目的就是描述含水层面对人为抽水和海洋潮汐振荡所呈现的特征。获取的结果显示,海洋潮汐对地下水位以及水的含盐度有重要影响。发现地下水位和潮汐水位的波动周期相同,具有明确的时间滞后。采用承压和半承压含水层含水层方法并通过分析时间滞后和振幅衰减率对水力扩散率进行了计算。结果表明,两个含水层之间的水力扩散率 存在差别。另外,存在明显的差别,取决于时间滞后或振幅是否进行了分析,可能是由于含水层内异质性的影响造成的。水电导率变化的详细研究揭示,日常的和相合的潮汐对地下水含盐度有重要影响。当水力扩散率较高时,水电导率变化就大,表明海平面振荡引起淡水/海水界面移动,因此影响着地下水含盐度。

Hidrodinâmica das águas subterrâneas e resposta da salinidade na maré oceânica em aquíferos costeiros: estudo de caso de Sahel Doukkala, Marrocos

Resumo

Variações sazonais do nível do mar tem um impacto enorme nos níveis das águas subterrâneas e na salinidade. Consequentemente, eles causam mudanças espaço-temporais na interface água doce/água salina. O efeito das marés oceânica da dinâmica das águas subterrâneas e da salinidade foram investigados em aquíferos costeiros de Sahel Doukalla, Marrocos. Monitoramento contínuo do nível de água e condutividade elétrica (CE) foi conduzido em dois poços costeiros (retirados de dois aquíferos diferentes) por um período de 9 meses. O objetivo principal do estudo foi caracterizar a exposição dos aquíferos às operações de bombeamento antrópico e oscilações de maré oceânica. Os resultados obtidos mostraram que a maré oceânica tem um efeito significativo no nível das águas subterrâneas assim como na salinidade da água. Os períodos de flutuação do nível das águas subterrâneas e nível da maré foram encontrados em igualdade, com tempo de diferença especifico. A difusividade hidráulica foi calculada utilizando ambos métodos de aquíferos confinados e semiconfinados e pela análise de ambos os tempos de diferença e amplitude do fator de decaimento. Os resultados indicam diferentes difusividades hidráulicas entre os dois aquíferos. Além disso, houveram diferenças aparentes dependendo em se o tempo de diferença ou amplitude foram analisados, possivelmente devido à efeitos da heterogeneidade nos aquíferos. Um estudo detalhado da variação CE das águas revelou a influência significativa da maré sinódica e diária na salinidade das águas subterrâneas. As variações CE na água foram significantes quando a difusividade hidráulica é maior, indicando que as oscilações do nível do mar induzem o movimento de interface água doce/água salina e consequentemente influenciaram a qualidade das águas subterrâneas.

Notes

Funding information

This study received financial support from Franco-Moroccan Mixed Committee (MA/08/191) in charge of the Hubert Curien Partnership (PHC) Volubilis project.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Team of Water and Environmental Management (G2E), National School of Applied Sciences (ENSAH)University Mohamed 1stAl-HoceimaMorocco
  2. 2.I2M UMR 5295 Laboratory, Environmental Civil Engineering DepartmentBordeaux UniversityBordeauxFrance
  3. 3.Marine Geoscience and Soil Science Laboratory, Earth Sciences DepartmentUniversity of Chouaïb Doukkali, Faculty of SciencesEl JadidaMorocco

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